In modern rotor spinning machines, there is always the demand for the highest possible production capacity, in order to be able to optimally utilize the spinning machine and to operate it in a cost-effective manner. Therefore, attempts were made in the prior art to be able to increase the rotor speed and thus the delivery speed, and thus to achieve higher production. However, such an increase in the production speed is limited by the increase in the delivery speed, since an increase in the delivery speed also always entails a reduction in machine efficiency, which in turn reduces production capacity. For example, a higher delivery speed also leads to an increase in the thread breakage frequency, and thus to a temporary failure of the spinning unit. As such, with known spinning machines, the delivery speed was adjusted manually based on previous experience, in such a manner that reasonable machine efficiency was obtained. Thereby, whether good production can be achieved through the manual selection of the delivery speed depends both on the experience of the operator and on a multitude of other influences that are not always foreseeable.
As such, in order to increase the production capacity of an open-end rotor spinning machine, DE 10 2011 112 364 A1 proposes to detect the number of thread breaks on the rotor spinning machine, and to automatically adjust the rotational speed of the spinning rotors as a function of the respectively determined thread breakage rate. The thread breakage rate should always be within a predetermined desired range, and below a maximum thread breakage rate. The maximum acceptable thread breakage rate arises from the quality requirements of the respectively produced yarn and from the capacity of the rotor spinning machine to eliminate thread breaks. As a result, a high-quality yarn can be produced with good productivity of the rotor spinning machine. Since, when the maximum permissible thread breakage rate is exceeded, the rotational speed of the spinning rotors is always reduced and production is thus limited, the yarn production capacity of the rotor spinning machine cannot be utilized in an optimum manner.